1. Field of the Invention
The present invention relates to subterranean barriers for waste management formed by improved methods, apparatuses, and systems. Particularly, the present invention relates generally to methods, apparatus, and systems for joining adjacent casing sections positioned within respective subterranean boreholes. For example, the present invention relates to methods and apparatus for joining, via at least one weld, a plurality of casings to one another to form a substantially continuous barrier.
2. State of the Art
Containment, management, and disposal of various types of waste, such as chemical, nuclear, and other potentially harmful types of waste are recognized, longstanding problems. It is also well recognized that buried waste may often include heavy metals such as mercury or cadmium, carcinogenic materials such as trichloroethylene, radioactive materials, or other hazardous substances. Such hazardous materials within buried waste may be leached (i.e., carried from the waste within a liquid) therefrom, into surrounding soil and into the groundwater. Because water is used for human consumption and for agriculture, contamination of groundwater by leaching is a major concern.
However, the contamination caused by buried waste may not be limited solely to groundwater. For instance, contaminated groundwater may be carried into other waterways such as streams, rivers, and lakes, thus polluting those waterways and leading to poisoning of plant and animal life. In addition, polluted waterways pose a threat to humans as well, particularly in the case of waterways and bodies of water used for recreational purposes or as sources of drinking or irrigation water.
Also, while many of the problems associated with buried waste arise from the effect of leachate on water systems, buried waste may also emit gas phase contaminants that may cause deleterious effects if not contained and managed. For instance, such gas phase contaminants may pollute the soil and the groundwater, and may build up to unsafe concentrations or pressures, if contained, which could ultimately result in an explosion, or pollution of the atmosphere by venting of the gas.
Accordingly, a variety of methods and devices have been devised to attempt to resolve the problems related to buried waste. These remedies may be broadly grouped into the categories of remediation and containment. Generally, remediation focuses on processes designed to change the chemical composition of a contaminated material or contaminant to a more benign chemical composition, while containment remedies seek to isolate contaminants and contaminated material within an area or remove them from an area.
Remediation approaches such as biological treatments, thermal processes, and chemical processes may be problematic for a variety of reasons. In particular, many remediation techniques may be expensive and potentially hazardous. Further, it may be difficult to verify the effectiveness of many remediation treatments. Also, determining the proper or optimum remediation technique for a given contamination scenario may be, in itself, a complex and time-consuming process.
Containment, barrier, or in situ, approaches may be problematic as well. One known containment approach is simply to dig up and remove the contaminated soil for treatment or disposal. This approach is expensive and time-consuming and often accomplishes little more than moving the problem to another location. Of course, finding an acceptable ultimate disposal location is another significant impediment to movement of a contaminated region. Other containment approaches involve installing vertical barriers, horizontal barriers, or both types of barriers around the buried waste. In theory, this approach is attractive because it does not require digging up or otherwise disturbing the buried waste.
However, conventional containment or barrier systems suffer from a variety of inadequacies including a lack of durability, corrosion resistance, and structural integrity. These inadequacies are a function of numerous factors associated with the environment in which the containment or barrier systems are located including, but not limited to: exposure to harsh chemicals such as concentrated saline solutions, saturated calcite and gypsum solutions; exposure to extreme thermal gradients; and exposure to stresses induced by shifting in the earth within and adjacent the contaminated area. In addition, conventional barrier systems may suffer from inadequate ability to monitor or verify the integrity thereof as well as inadequate reparability thereof if a failure should occur.
Accordingly, recently, containment systems that are designed to contain, collect, or process effluent which would otherwise escape from a zone containing waste materials, have been developed. One such containment system is disclosed in U.S. Pat. No. 6,575,663 to Kostelnik, et al., assigned to the assignee of the present invention, the disclosure of which is incorporated in its entirety by reference herein. More particularly, U.S. Pat. No. 6,575,663 discloses a barrier comprising a series of adjacent casing strings that are interlocked with one another and may be filled with a barrier filling material to form a substantially continuous wall. Casing strings are disclosed as being disposed within the subterranean formation by way of so-called “microtunneling” techniques.
For instance, a barrier is first installed underneath the zone of interest. Specifically, a line of individual steel casing sections are placed by a micro-tunneling device or the like which simultaneously excavates a tunnel and installs connecting casing segments behind the micro-tunneling device as tunneling progresses. The length of the tunnels is determined by the size of the zone of interest to be contained. Preferably, the tunneling device includes a system for ensuring accurate placement and orientation of the tunnels and casing sections. As each tunnel is dug and lined with casing sections, a successive adjacent tunnel is dug and casing sections situated therein which longitudinally interlock with the casing sections placed in the previously excavated tunnel, so as to form a continuous barrier of predetermined width.
The casing sections, the joints whereby they interlock adjacent casing sections, or both may be filled with a filler, such as a grout or the like, for providing an added measure of strength, durability, and imperviousness to the barrier. In a preferred embodiment, two vertical barrier sections are interlocked with the ends of a horizontal barrier section so that the horizontal barrier and vertical barriers collectively form a continuous U or channel-shaped containment boundary extending around the zone of interest.
However, the integrity of such a barrier may, prematurely, fail due to repeated thermal stresses, or movement of the casing strings within the subterranean formation. For instance, filler within the casing sections may crack, or may otherwise become infirm.
In view of the foregoing problems and shortcomings with existing barrier apparatus, methods, and systems, it may be desirable to provide improved methods, apparatus, and systems in relation thereto. Also, it may be desirable to form barriers for waste management by such improved methods, apparatus, and systems.